Recently, high heat resistant thermoplastic resin compositions have been used for parts of light emitting diodes (LEDs). LEDs have rapidly replaced existing plenty of light sources because of their excellent energy efficiency and long life. The high heat resistant thermoplastic resin is used for parts of LEDs including a reflector, a reflector cup, a scrambler, a housing, and the like. For example, a high heat resistant modified-polyamide-based resin, that is a PPA (polyphthalamide)-based resin, can be used as the high heat resistant thermoplastic resin, wherein the high heat resistant modified-polyamide-based resin is reinforced with glass fiber and includes an aromatic ring as a part of its main chain.
The high heat resistant thermoplastic resin should have properties such as tolerance for high temperatures generated during the manufacture of LEDs, high initial whiteness index, and excellent reflectance to be used as parts of LEDs. Simultaneously, the consistent irradiation of light sources causes yellowing, and such yellowing reduces whiteness index. Thus the high heat resistant thermoplastic resin should also minimize such reduction of whiteness index. Non-electro conductivity may also be necessary for the high heat resistant thermoplastic resin used in LEDs.
A reflector, one part of a LED, may be made of various materials, for example, ceramics or heat resistant plastic. Productivity is a problem for the ceramics, and reduction of optical reflectance due to color change is a problem for the heat resistant plastic in case of injection molding, sealant thermal curing, or under actual environmental conditions. Also, when parts of LEDs with complicated and small structures are injection molded, insufficient moldability disturbs thin film molding.
Korean Patent Publication No. 2012-0066740 discloses a polyamide resin composition stated to have excellent reflectance and impact resistance by applying a white pigment, sodium phosphate salt, and glass fiber to a polyamide resin. However, it describes a wide range of amounts of inorganic filler, and an excessive amount of the inorganic filler can reduce surface gloss and moldability thereof.